As is known in the art, motion compensation in body or neuro MR involves acquisition of low-resolution 2D or 3D image data and performing bulk registration of all features in the image to derive a transformation matrix to adjust the scanner's slice position. In the case of coronary motion compensation, the state of the art involves performing a 1D MR image with high temporal resolution to monitor the bulk motion of the diaphragm. In this case, 1D acquisition is used in place of 2D to attain sufficient temporal resolution. This diaphragm motion in turn is assumed to be linearly correlated with the motion of the heart, and in turn to be linearly correlated with the motion of the individual coronary arteries. However, clinical results and other studies analyzing cardiac and coronary motion clearly show that this is a false assumption, leading to blurring and motion artifacts when imaging the coronary arteries.
Several attempts to address the problem of determining motion of the heart for the purpose of imaging the coronary arteries have been suggested. One technique is sometimes referred to as an adaptive navigator technique. With such technique, raw data acquisition based on the motion magnitude is obtained and the location modified in k-space to minimize motion effects. There are also slice-following techniques that move the slice position of the scan based on motion detected by a 1D navigator.
Another suggested technique is sometimes referred to as a multiple navigator technique. Here, motion derived is used not only in one direction, but also from 3 directions to assess motion of the heart in 3D. This method still assumes that heart motion and coronary motion are correlated, and that there is no change in position between the time of the navigator measurement and the image acquisition.
Still another suggested technique uses low-resolution measurement and tracks bulk heart motion which, combined with 3 navigators, corrects for motion in 3 dimensions. The disadvantage of this method is that the 3D heart motion model is derived at a single time-point and not updated during subsequent high resolution scanning of the coronaries. In addition, it still assumes correlation between heart motion and coronary motion, and that the heart cycle length, and motion of the heart within each cycle is relatively constant. Such techniques are described in one or more of the following papers: “Novel Prospective Respiratory Motion Compensation Approach for Free-Breathing Coronary MR Angiography Using a Patient-Adapted Affine Model” by Dirk Manke, Kay Nehrke and Peter Boernert, published in Magnetic Resonance Medicine 50:122-131 (2003); “A Study of the Motion and Deformation of the Heart Due to Respiration” by Kate McLeish and Derek L. G. Hill, published in the IEEE Transactions on Medical Imaging, Vol. 21, No. 9, Sep. 2002; A Model Evaluation and Calibration for Protective Respiratory Correction in Coronary MR Angiography Based on 3-D Image Registration” by Dirk Manke, Peter Rosch, Kay Nehrke, Peter Bornert and Olaf Dossel, published in the IEEE Transactions on Medical Imaging Vol. 9, Sep. 2002; and “Respiratory Motion in Coronary Magnetic Resopnance Angiography” A Comparison of Different Models”, by Dirk Manke, Kay Nehrke, Peter Bornert, Peter Rosch, and Olaf Dossel, published in the Journal of Magnetic Resonance 15-661-667 (2002)/